This is topic EQ'ing a CP50 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Geof Abruzzi (Member # 1312) on 11-12-2002, 04:49 PM:
I have several questions concerning our Dolby CP50. We are installng new speakers in our theater, and I want to re-EQ once they're in. Unfortunately we haven't got a pink noise card, and we don't have an extender either (to be able to adjust the EQ's with them out of the box.) The only prices for these items I've found are higher than our non-profit will currently allow ($350+ each).
My easier question would be if anyone knows a good souce for things like these used (and cheaper). Alternatively, I have an RTA with a built in signal generator. Is it possible to use this rather than the card? If so, should I bring it in through one of the projector inputs, or somewhere else? Any info on this would help greatly.Geof
Posted by Gordon McLeod (Member # 33) on 11-12-2002, 04:54 PM:
The Cp50 varries in the backplane design If it has the daughter board on the back then yes an external pinknoise source can be injected for the lcr channels but not the sub
Posted by Aaron Sisemore (Member # 145) on 11-12-2002, 07:10 PM:
Unfortunately, however you are basically screwed unless you have the extender cable adaptor, otherwise an EQ job will take many many many hours of unplugging the Cat 64, making a tweek, plugging the 64 back in, looking at the RTA, unplugging the 64, making another tweek, plugging the 64 back in, etc etc etc...Bringing the pink noise thru the projector input would not be recommended as it has to pass thru the NR and signal processing stages, and will be impossible to isolate individual channels as you can with the cat. 85C.
See if you can locate a technician's services to get the EQ done properly. It will likely cost less than the components you require to do it yourself.
-Aaron
Posted by Steve Kraus (Member # 476) on 11-13-2002, 01:35 AM:
It's not that difficult to inject a signal into the middle of the CP50. Do you have a Cat.160 subwoofer card or is that slot filled with a blank (except for some traces) card called a 110L? (That's even assuming you have a Cat.150 2:4 channel decoder and not the old 110 & 116.)
If you are set up with no subwoofer card and the link card, the link card jumpers Left-Total and Right-Total across that gap. BUT, to use the Cat.85C pink noise generator you'd plug it into the 110 slot and the link card then gets reversed (note the edge connectors on both ends) and plugged in in place of the Cat.150 to jumper L,C,R,S across the gap where the 150 decoder was. So for starters, you might consider tack soldering a connection right on the "150" end of the 110L link card:
L is on the contact 10 - contact 4 connection, C is 8/5, R is 7/6 and S is 2/1. Inject your signal there. An alternative is to tack onto 1,4, 5 and 6 of the 150 connector on the backplane.
As for extenders, you can live without it although it's awkward. You ought to be able to reach into the CP to adjust the pots "live" on the R and possibly on C with the card in place and the neighbors to the left out, depending on the size of your hand. In fact, with the 150 and 110L out (hooking onto the backplane) you can probably adjust L as well.
I think the meter card can come out for this but the Cat.22's must remain in because Dolby availed itself of a line drive amp found on each Cat.22 card (those cards are also used in recording studio gear) and thus the Cat.117 fader/output card contains line drive amps only for C and S while L and R get sent back to the Cat.22's on board amps and then to the output terminals.
Posted by Geof Abruzzi (Member # 1312) on 11-14-2002, 09:13 AM:
Thanks, this is is the information I need. It looks like I can tap into the backplane from the back of the unit since all the pins for mounting the connector are visible from there. I was also wondering what level the signal should be at?On a related not, does anyone know a tech in southern New Mexico, or El Paso?
thanks.
Geof
Posted by Antonio Marcheselli (Member # 373) on 11-18-2002, 05:03 AM:
What about equalizing a CP65 without a pink noise card? Is it possibile to feed pink noise into each channel?
Bye
Antonio
Posted by Pete Naples (Member # 761) on 11-18-2002, 05:14 AM:
Antonio,
Yes, one could inject pink noise via the 6 channel input intended for use with a Dolby Digital processor (DA20). I don't know what the correct level is off hand though.
Posted by Antonio Marcheselli (Member # 373) on 11-18-2002, 05:33 AM:
Great!
I really don't know much of CP65: does it have a 6ch input by default? I would like to help a friend of mine that manage a small theater outside the town that actually cannot afford a tech for equalization. He told me that the sound is very poor and I would like to help him. Can anyone help me about the input level?
Antonio
Posted by Pete Naples (Member # 761) on 11-18-2002, 06:13 PM:
All CP65 have a six channel input. However it won't work fully unless there's a Cat443 installed. Lack of Cat443 wouldn't prevent you from injecting pink noise though, assuming the right level!
Posted by Antonio Marcheselli (Member # 373) on 11-18-2002, 07:31 PM:
Pete,
I'll check for the 443.
In case there is the 443, I have few questions:
1. Should the pink noise recorded at -20dbFS?
2. Should the SUbwoofer pink noise recorded band limited?
3. I do not have the extender for the eq cards. Can I build it by my own? Can I remove the EQ cards while CP is powered (with just the fader set to 0)?
I hope that there is the 443, it will be my first equalization! ![[Smile]](smile.gif)
Bye
Antonio
Posted by Michael Schaffer (Member # 1204) on 11-19-2002, 10:29 AM:
Probably not a very good idea, but in absence of other means, what about using the pink noise test loop for the slit loss to eq the left and right channel, then copy the settings to the center channel?
Posted by John Hawkinson (Member # 1135) on 11-19-2002, 01:45 PM:
At that rate, you might as well swap cards.
--jhawk
Posted by Antonio Marcheselli (Member # 373) on 11-19-2002, 02:05 PM:
Pete,
I'm not familiar with the CP65 so I've read the manual to understand the B-Chain procedure.
Cat 443 is listed as a logic card that configures the CP for the selected format. It is not listed as optional.
Are you sure that Cat 443 is optional and needed for Digital inputs?
Ciao
Antonio
Posted by Pete Naples (Member # 761) on 11-19-2002, 05:55 PM:
My sincere apologies.
When I typed Cat443, I should have typed Cat441. There is quite a difference!
If it doesn't have a Cat441, you can still do the 'B' chain via the 6 channel input, you just can't align Right Surround and Subwoofer, as there will be no Right Surround or Subwoofer output. As no card = no Rs/SW, then there's no need to worry about it's presence!
Posted by Gunter Oehme (Member # 499) on 11-19-2002, 07:50 PM:
Antonio, Pete,
you can use the analog inputs for digital sound formats.
The pink noise signal should have a level of 380 mV RMS.
The limitation is that sub woofer input will be in digital mode i.e. +10 dB inband.
For setting the level of the optical (analog) sub woofer the 6 channel input cannot be used. For this purpose the pink noise signal needs to be injected at the connector of the Cat 441 on the backplane.
Pulling the Cat 64 for all adjustments make only sense if small corrections are needed.
However you could try move the pots while the Cat 64 is installed. Just remove the Cat 222 and 150 and use only one Cat 64 at a time.
Michael,
using the pink noise loop for slit loss film in the regular signal path is really not a good idea.
In mono format the academy filter is in the signal path.
In the Dolby formats the pink noise signal will be not linear after Dolby A or SR decoding.
Posted by Michael Schaffer (Member # 1204) on 11-19-2002, 09:06 PM:
Yes, that`s why I suggested equalising L and R and then copying the settings to C. Can the NR not be switched off on the CP50?
Posted by Antonio Marcheselli (Member # 373) on 11-20-2002, 05:58 AM:
Pete and Gunter
Thanks a lot for your help. I've asked to my friend toi check for 441, but since his theater has a subwoofer I believe that there is one!
Yes, I thought to use one eq card a time too to have my hand space enough to move the pots. Can the EQ card be removed without turning off the CP (muting it before)?
About the level: how can a pink noise be at 380mV? I can make a 1000Hz note at 380mV but what about the pink noise? DTS pink noise is -20dB FS. However it is not so important, eventually the reference fader position will be not exactly at 7.0...
About analog subwoofer, where exactly I have to connect my pink noise on the backplan?
Bye
Antonio